1. Field of the Invention
This invention relates to a scraping tool, and more particularly, to an improved apparatus and method for preparing the outer surface of polyethylene conduits in keyhole excavation operations for natural gas and water lines, as well as underground fluid lines.
2. Description of the Prior Art
Metal conduits, particularly iron or steel conduits, have been used in various applications, including the distribution of natural gas and water through service lines. These conduits or pipes are connected together typically by conventional joining methods, such as welding. The joining methods typically require one or more machining, cutting, polishing, grinding, scraping, or cleaning operations. Various devices have been disclosed to perform these types of operations.
U.S. Pat. No. 5,549,024 discloses a clamshell machining lathe for cutting and finishing pipes in industrial settings. The lathe includes a pair of annual members, including a stationary member for clamping and a rotatable member for cutting and finishing. The stationary member attaches to a pipe. The rotatable member rotates around the pipe. A cutting tool and an end finishing tool extend from the rotatable member to perform cutting and finishing operations on the pipe. The end finishing tool is advanced manually in a longitudinal direction along the length of the pipe through the use of a crank wheel. Alternatively, the end finishing tool is advanced using a step motor.
U.S. Pat. No. 6,786,118 discloses a device for machining a shaft. The device includes a frame support and a tool support. The tool support is mounted on the frame support to move a tool in a longitudinal direction relative to the shaft via a worm drive.
U.S. Design Pat. No. D492,950 discloses an ornamental design for a journal turning lathe. The lathe includes a plurality of annular rings connected to a plurality of cylindrical, longitudinal members. The annular rings appear to be designed to surround a shaft or pipe for machining.
Various devices have been disclosed for performing grinding or shaving operations to facilitate the welding of metal conduits. U.S. Pat. No. 4,934,109 discloses a grinder assembly having a body portion that includes a pair of legs extending therefrom. A shaft also extends from the body and has a grinder section that includes a body, a grinder, a grinding wheel, and a wheel rotating device. The grinding wheel performs a grinding operation to provide a V-shaped bevel.
U.S. Patent Application Publication No. 2002/0129684 discloses a pipe shaver. The piper shaver includes a cutting blade, housing, lifting means, a lever, and a threaded cam. The lever manually urges the blade radially outwardly away from the pipe. The threaded cam moves a cutting edge on the cutting blade longitudinally along the outer diameter of the pipe to shave a thin, substantially uniform layer of material from the outer diameter of the pipe.
Various portable machining or joining devices have also been disclosed. U.S. Pat. No. 5,054,342 discloses a portable pipe machining apparatus for cutting pipe or preparing the end of a pipe for a subsequent joining operation, such as welding. The pipe machining apparatus includes a frame that includes two joined semicircular sections for radially surrounding a pipe. A tool carrier is rotatably mounted on the frame by a plurality of roller bearings. The tool carrier includes a pair of cutting tools that rotate about the pipe. The apparatus also includes a bearing means that can be adjusted between the frame and the tool carrier to compensate for the wear of individual bearings during use.
U.S. Pat. No. 4,091,514 discloses a machine tool for preparing the end of a pipe in a subsea location for receiving an overfitting coupling. The tool includes a support beam assembly and a remotely operable hydraulic pipe clamp for clamping the pipe. The support beam assembly supports an axially movable carriage, a split frame, and a split ring gear. The split ring gear forms a spool assembly. A face plate extends from the spool assembly. The face plate includes a milling machine for milling the pipe surface and sensing tool for monitoring the milling machine.
Plastic conduits, particularly polyethylene conduits, have been replacing iron and steel conduits in the distribution of natural gas, water, and other fluids through service lines. The metal composition of iron and steel conduit that is used in underground applications makes it susceptible to corrosion and deterioration due to cathodic action. Polyethylene conduit used for natural gas and water service provides the long term benefits of corrosion resistance and durability.
Not only is polyethylene used to fabricate gas pipelines, it is also used in the fabrication of valves, fittings, couplings and the like for controlling gas flow through the pipelines. The joints between pipelines and polyethylene valves can be connected by butt fusion and electrofusion to eliminate the need for conventional threaded connections and fastening nuts. U.S. Pat. No. 5,639,394 discloses a polyethylene valve assembly formed by electrofusing a coupling to pipe end fittings.
Plastic pipes, pipe end fittings, couplings and valves typically undergo cleaning operations before being joined. Various portable cleaning methods are well known. Japanese Patent Document No. JP 10024272 A discloses a method for cleaning a polyethylene pipe for subsequent electrofusion. Sheet material is impregnated with organic solvents and housed in a hermetically sealed container. A worker removes the sheet material from the container at the worksite and wipes the pipe outer surface to prepare the surface for electrofusion.
U.S. Patent Application Publication No. 2004/0188013 discloses a pipe fusion device that includes a cleaning mechanism. The cleaning mechanism includes a pair of plates that form a retaining mechanism. The retaining mechanism holds a flexible wiper that cleans the outer surface of a pipe that has been inserted into the pipe fusion device.
U.S. Pat. No. 5,894,772 discloses a portable polyethylene pipe machining tool for cutting plastic pipe. The tool includes a fixed cylindrically-shaped frame that is attached to a polyethylene pipe for cutting and finishing and a rotatable frame that rotates relative to the fixed frame. The tool also includes a parting tool assembly that performs scraping and finishing operations. The parting tool assembly moves longitudinally along the pipe outer surface during the scraping and finishing operations.
U.S. Patent Application Publication No. 2005/0022353 discloses a portable plastic pipe cutter. The cutter includes a table for supporting a pipe, means for rotating the pipe relative to the support, and a cutter for cutting the pipe during rotation. The rotating means utilizes a scissor mechanism having pressure wheels to rotate the pipe. The cutter includes a cutter saw and a handle.
The process of joining underground pipes through electrofusion and other means typically requires significant excavation of the ground around the joint. U.S. Pat. No. 5,624,206 discloses a platform for supporting pipes during an excavation. The platform includes a pair of flat rectangular shoring members with support braces attached thereto. The platform also includes a jack member for pushing against the sides of the excavation. A pair of clamps extends from the support braces to connect the pipes to the platform.
U.S. Pat. No. 5,430,921 discloses a cutting apparatus for a pipe that includes a frame formed from two parallel longitudinal members connected by end beams. Each end beam is attached to a chain that encircles the pipe. A cutter unit is mounted on one of the longitudinal members.
The excavation operations cause considerable disruption to the surrounding landscape. The operations also limit the location of underground pipes with respect to buildings. Various devices for facilitating the joining operations of underground pipes have been disclosed. Accordingly, it is particularly desirable to minimize the disruption to the surrounding landscape.
The need to minimize disruption to the surrounding landscape has led to the development of minimally invasive technology or “keyhole” excavations. The objective of keyhole excavation is to perform as much work underground with the smallest possible ground opening. The target holes are typically 18 inches in diameter but may be as small as twelve inches in diameter. The technology to cut pavement coupons and excavate downwardly to a pipe section for joining is well-known. Accordingly, there is a need for improved keyhole excavation devices.
U.S. Pat. Nos. 5,364,207 and 5,613,807 disclose a method and an apparatus for making service connections to polyethylene pipe. The method involves excavating a hole that is less than two feet in diameter to locate the pipe for connection. An electrofusion apparatus and a polyethylene pipe for connection are introduced into the hole. The electrofusion apparatus including a heating element is positioned on top of the polyethylene pipe. An opening is drilled into the polyethylene pipe through the fused stack to allow the polyethylene pipe to be fused. The heating element and fused stack are withdrawn.
U.S. Pat. No. 6,669,406 discloses an apparatus for cleaning the surface of an underground polyethylene pipe in preparation for an electrofusion operation. The apparatus includes a handle and a milling assembly. The milling assembly includes a rotatable cutter that is mounted on a plate. However, the cutter only rotates 180° around the outer surface of the pipe to perform the milling operation, so that there is an inherent risk that the outer surface will not be concentric. Therefore, any variations in the concentricity or roundness of the external surface of the pipe must be corrected before the milling operation is performed. Accordingly, there is need for an improved method and apparatus for preparing polyethylene conduits for repair using keyhole excavation operations for underground fluid lines.